Phase-Manipulated Calcium Borate-Based Multicolor Mechanoluminescence

Multicolor mechanoluminescence (ML) materials have attracted growing attention for applications in anti-counterfeiting, smart skin, wearable electronics, and structural health monitoring. However, their widespread implementation remains significantly hindered by the scarce available compositions and harsh preparation conditions-typically requiring temperatures above 1000°C and protective atmospheres. Here, a facile, low-temperature, and atmosphere-free synthesis of calcium borate-based ML materials (Ca₂B₂O₅ and CaB₂O₄) is achieved. The phase ratio of Ca₂B₂O₅ and CaB₂O₄ is manipulated by adjusting the stoichiometric ratio of raw materials (H₃BO₃ and CaO). The distinct tetrahedral and octahedral coordination of Mn²⁺ in these phases gives rise to tunable ML emission spanning from green to orange (535-605 nm). When incorporated into polydimethylsiloxane (PDMS) elastomers, these materials exhibit remarkable multicolor ML suitable for multi-level optical encryption and motion visualization. The encrypted information remains hidden under daylight or UV illumination can be deciphered only through ML activation, while the stress-induced color variation enables real-time monitoring of joint movement. This work not only establishes a versatile route for the design of low-temperature, phase-tunable ML materials but also reveals promising applications in next-generation information security and intelligent motion-sensing technologies.